Granular or powder explosives and their manufacture



Patented Feb. 1, 1949 TENT OFFICE GRANULAR R POWDER EXPLOSIVES AND THEIRMANUFACTURE John Whetstone, West Kilbride, Scotland, as-

signor to Imperial Chemical Industries Limited, a corporation of GreatBritain ber 15, 1941 Section 1, Public Law 690, August 8, 1946 Patentexpires September 15, 19.61

The present invention relates to granular detonating explosivecompositions of the kind in which the granules individually compriseammonium nitrate and an easily fusible organic explosive compound in astate of intimate admixture. The invention also relates to an improvedor simplified process for the production of such explosive compositions.

Explosives made in accordance with the invention are of improvedsensitiveness to initiation and the granules are of an unusually robustcharacter, as a result of which these explosives maintain well ontransport and storage the bulk density at which they are packaged andconsequently also maintain their sensitiveness well. The explosives madeaccording to the present invention include not only coarsely granularproducts but also those in which the granules are small, and which maybe described as powder explosives. They may be used for quarrying ormining or for demolition purposes, and can be initiated directly I bythe impulse of commercial detonators.

Blasting explosive powders containing ammonium nitrate and organicexplosive compounds are usually manufactured by grinding the solidammonium nitrate and the organic explosive together, even when, as inthe case of fusible aromatic nitro-compounds such as trinitrotoluene,the organic explosive compound is easily fusible. An additionalingredients of the composition are introduced during or subsequent tothe grinding operation. Prolonged grinding is required in order toproduce an explosive satisfactorily sensitive to initiation by acommercial detonator.

Military explosives containing ammonium nitrate and aromaticnitro-compounds can be made by coating solid ammonium nitrate with thefused aromatic nitro-compound, the explosive compositions so obtainedbeing compressed, or cast, or cast and compressed, into the ammunitionin which they are to be used. They are, however, not sensitive toinitiation by ordinary detonators, and in eifecting their detonation itis necessary to employ an intermediate primer or booster whereby thedetonating impulse transmitted from the detonator is enhanced. Thedensity of such charges usually exceeds 1.4 and their velocity ofdetonation and their negative oxygen balance are-usually higher than isdesirable for commercial blasting purposes.

The fusion temperature of ammonium nitrate is too high to enable it tobe safely melted with fusible organic explosive compounds, but it can bereduced by the inclusion of additional materials such as salts havingwater of crystallisa- 9 Claims. (Cl. 52-21) that form eutectic mixtureswith it. In the man ufacture of cast explosive charges, such materialsusuall of an oxidising or reducing character, have been included inmelts comprising ammonium nitrate and fused organic explosive compounds,with the object of minimising the content of the organic explosivecompound required to yield a composition that is sufficiently fluid tobe conveniently loaded. These compositions, which contain ammoniumnitrate in a more or less completely fused condition, however, sufferfrom the defect that the liquified inorganic salts and the moltenorganic explosive constitute two immiscible liquids that can only becoarsely dispersed by agitation of the melt, so that the resultingmixture segregates rapidly before it solidifies, and the resulting castexplosive charges are of lower sensitiveness to initiation than thosemade by coating the solid oxidising salts with molten organic explosive,and may fail to propagate their detonation properly.

In the preparation of cast explosive charges such as are used forfilling containers, for example shells or other projectiles, grenades,mines and the like, it has been proposed with the aid of an emulsifyingagent to emulsify a highly explosive organic compound or compounds in amelt of an oxidising salt or salts, for instance ammonium nitrate, withor without metallic nitrates. According to this proposal, theemulsifying agent may be a colloidal substance soluble or swellable bywater and capable of increasing the viscosity of the melt, and theformation of the saline melt into which the high explosive organiccompound, for instance trinitrotoluene, is incorporated, may be assistedby the presence of hydrated salt, an organic amide or a small proportionof water, the resulting emulsified explosives being characterised byimproved sensitiveness to detonation and other advantages as comparedwith similar compositions made by a fusion process or partial fusionprocess Without the use of the emulsifying agent. One of theseadvantages is that compositions of sufiicient fluidity for loading intoammunition may be obtained at safe working temperatures e. g. to C. witha reduced proportion of. the fusible high explosive compound. Massivecast explosive charges produced according to the method of theaforementioned proposal, however, are insufiiciently sensitive to beinitiated by an ordinary commercial detonator, and are unsuitable forcommercial blasting purposes.

According to the present invention, in the mancooling atmosphere.

3 ufacture of detonating explosives suitable for commercial blastingpurposes, amolten easily fusible organic high explosive compound isfirst emulsified with the assistance of an emulsifying agent in a melt,comprising ammonium nitrate and a non-volatile compound adapted to lowerthe melting point of the ammonium nitrate, that congeals to form asolid-mass when cooled 4 there may be used water and anhydrous or lessfully hydrated forms of the hydrated salt. The saltsemployed areadvantageously of oxidizing character, and-metal nitrates and hydratedmetal nitrates such as calcium nitrate, tetrahydrate, lead nitrate,alkali ,metal nitrates, magnesium nitrate hexanitrate or the like mayconveniently "*by' use'd.

to a temperature higher than those at which'explosives are customarilytested for climatic storage, andthe resulting emulsion is congealed andgranulated.

According to one form of the invention the granulation is commencedbeiere'the'emulsion has cooled sufiiciently to become substantiallycongealed, for instance by congealing the emu1-,

after broken up into granules by mechanical action.

If theemulsion is granulated by first converting it into a thin sheet,this may be carried out by picking it up on a cooled rotating drum; andin this case also it may be necessary thatthe ammonium nitrate in thehot-emulsion should be completely liquified to allow it-to run somewhaton thedrum. The granulationmay be carried out breakingup the congealedcoating into flakes or The method ofgranulating' a" a coarse powder.congealing cake of the emulsion, however, does not necessitate the useof anemul'sion in which the ammonium nitrate has been completelyliquified. The congealed cake is frequently easier to crush while it isstill warm or even hot than when it has cooled to ordinary atmospherictemperature, and if it is allowed to coolcompletely its crushing isfacilitated by warming it.

On the other hand whenthe emulsion is congealed in the'iorm' of thinsheets it can easily be broken up "into flaky granules even at roomtemperature.

When the sheet or cake has been broken Tup, the product may be screenedto remove any particles that are too large or too small, andthewastefrom the screening operation may, if desired, be employed informinganother batch -of emulsified material. The size of the granulesmay be controlled by varying the intensity ofthe mechanical action inbreaking up the congealed cake, and it will be understood that theinvention includes not only explosive compositions of coarsely granularform but also explosive compositions in which the granules are small,and,

which may be described as powders.

For the purpose of the presentinvention, there may be used asnon-volatile compounds adapted to lower the melting point of ammoniumnitrate anhydrous compounds capable of forming low or in addition, theremay be employed hydrated;

salts that maintain their water of crystallization at temperatures atwhich explosives are cus tomarily tested for climatic storage, and itwill be understood that instead'of such hydra'ted'salts Whennon-volatile compounds adapted to assist the fusion of ammonium nitratewhich are not of an oxidising character are employed, for instanceanhydrous sodium acetate, sodium benzene sulphonate, sucrose, acetamide,urea or dicyandiamide, 'it is usually desirable to employ oxidising"salts alongwi'ththem. Theamount of the substance or substances adaptedto lower the melting poin't'oi the ammonium nitrate should be slim ycierit to render themelt sufficiently fluid to enable the emulsificationto be carried out at a temperature sufficiently low to avoid any dangerof un-,- controllable decomposition, and preferably at-a I temperaturebelow1O0 'C., but it is not necessary that'the whole of the ammoniumnitrate'should,

be liquifi'ed'so long as the emulsio n is suihciently Y employedcolloidalsubst'ances soluble or sw'ellable' melting eutectic mixtureswith it. Alternatively,

1 scopic nature.

fluid to manipulate. -If desired, the-emulsification may beassisted bythe addition'of an amount of-w-ater in excess of that'whichWill-becombined in the form of a crystalline hydrate when'the emulsionis cooled, but in this'case itis'desirable that the =excess watershould-be substantiaily evaporated away 'beforethe emulsion-solidifies.

As explosive-c-ompounds*there may advantageously be employed' solid highexplosiv'e'c'ompounds melting at temperatures-"not appreciably in excessof "the boiling'p'oint of waten but'whi'ch will. remain solid underoidinary -hot-* sto'rage conditions,-for instance trinitrotoluene 'ortetra-' nitroanisol, but there 'may also be employed mixtures'containing high "explosives 'othigher melting points, forexample;nexamtrbdipnnylamine, pentaerythrite' tetrariitrate;polyi'iitrophthaler'ies or the like, with'easily' fusible 'oreven'lidiiid 'explosiv'e com ounds in 'sflit'abl'e 1r)1opt)iti'orfs'.to" yield mixturesmat-mitts solidat hot' storage temper'atures' but liquify at temperatures not *sub stanti'ally above the b'oiling point ofwater. It is usually convenient to carryout theemulsification at atemperature between C. and C.

Asemulsifying agents there are-advantageously by water andcapable'ofinoreasing the viscosity of the hotaqueousammoniunfinitratesolution,

for instance agar-agar, carageen moss'extract; flour, de'xtrin,sodiumicellulose'glycollate, starch and various gums, e. g. gum arable;gum 'trag'aca'nth, "or gum tragon.

tween 0.3 per cent. and 0.7 per 'centl'of th"d1-Y Weight of theemulsion.

If desired; other ingredients of various types commonly employed in themanufacture'ofexplo'sivec'onipositions"may be introduced into thecomposition of the emulsionor mixed with-the granules. These aredesirablybf a- -non-hyg-ro- Examples of such materials inelude, forinstance; oxidisable ingredients suchas metal powders or carbonaceousingredientscooling or'fiarne quenching ingredients, waterproofing agentsand so forth. The composition -of--the final explosive should be soadjusted that-it has a desirable oxygen balance taking-intoaccou-nt anywrapping 1 or packing" material that will -"be included in; the blastingcharge.

The sensitiveness to the initiating of an exp10-- The quantityfof theemulsifying agent require'd will usually lie"besive of any givencomposition made in accordance with our invention, and also its velocityof detonation, may be controlled to a considerable extent by the bulkdensity at which it is packed; and this in turn depends largely in thesize of the granules, but, in general, explosives sufiiciently sensitiveto be initiated directly by commercial detonators are obtained even atunusually high packing densities in relation to those customarily usedfor ammonium nitrate powder explosives.

The invention is further illustrated by the following examples, in whichthe parts are parts by weight.

Example 1 A mixture of 8.4 parts calcium nitrate tetrahydrate and 5.6parts sodium nitrate are fused together and 65.6 parts ammonium nitrateand 0.4 part agar-agar are introduced in portions into the melt, whichis heated in a steam jacketed vessel until no more of the ammoniumnitrate dissolves. 20 parts molten trinitrotoluene are then stirred intothe mixture, which is kept at a temperature of at least 90 during theemulsification. The emulsion is then poured out to form a slab about onequarter inch in thickness, which is allowed to solidify, and is crushedwhen it has cooled to about 40 C. by means of a roller until it has beenbroken up into granules. The granules passing a 20 mesh British StandardSpecification screen and those retained by a mesh B. S. S. screen aresent for remelting. The granules passing a 15 mesh and retained by amesh B. S. S. sieve when packed under a pressure of 75 lbs. per squareinch yield a granular explosive composition of bulk density about 0.9capable of direct initiation by a No. 2 mercury fulminatepotassiumchlorate detonator. It has a power amounting to about 78 per cent. ofthat of blasting gelatine.

Ewample 2 The procedure is the same as in Example 1, except that theslab of the congealed emulsion is further crushed and only the particlesretained by a mesh British Standard Specification screen are sent forremelting. When packed under a pressure of 75 lbs. per square inch theresulting powder explosive has a bulk density of about 1.15, and issensitive to initiation by a. No. 3 mercury fulminate-potassium chloratedetonator. In a test in which two 1%" x 3" freshly made cartridges ofthe same explosive packed in waxed paper wrappers at the aforesaid bulkdensity are placed in line at varying distances in a common paperwrapper, the second cartridge is detonated by the first at a distance of2" but not at 3". Under the impulse of a No. 6 mercuryfulminatepotassium chlorate detonator it detonates at a velocity ofabout 3,810 metres per second.

Example 3 7.2 parts calcium nitrate tetrahydrate and 4.8 parts sodiumnitrate are fused together, 55.6 parts ammonium nitrate and 0.4 partagar-agar are introduced into the melt, and 17 parts trinitrotoluene areemulsified in the mixture at a temperature of 90 C. by the method asdescribed in Example 1. 15 parts of aluminium powder are then stirredinto the mixture, which is poured out and allowed to congeal in the formof a A" slab. The slab is then crushed under a roller at C. and only theparticles retained by a 20 mesh B. S. S. sieve sent for remelting. Theresulting powder explosive is packed in waxed paper containers under apressure of '75 lbs. per square inch, and has a bulk density of about1.07. When initiated by a No. 6 mercury fulminate-potassium chloratedetonator it detonates at a velocity of about 3,600 metres persecond,and in the aforementioned double cartridge test the second cartridge isdetonatedby the first at 3" but not at 4". This explosive can also beinitiated by a No. 2 mercury fulminate-potassium chlorate detonator. Theexplosive has a power amounting to about per cent. of that of blastinggelatine.

Example 4 toluene are emulsified therein, as described in,

Example 1, except that the emulsification temperature is at least C. Theemulsion is further heated to about 105 C. and poured out so as tocongeal into the form of a A" slab and is then crushed at a temperatureof 40 C., only the particles retained on a 16 mesh B. S. S. sieve beingsent for remelting. When packed in waxed paper containers under apressure of 50 lbs. per square inch the resulting granular explosive hasa bulk density of about 1.05. When freshly made cartridges of thisexplosive are tested in the aforesaid double cartridge test, the secondcartridge is initiated by the first at 4" but not at 5", and after thecartridges have been stored for one month the second cartridge isinitiated by the first at a distance of 5" but not at 6". This explosivehas a power amounting to about 82 per cent. of that of blastinggelatine, and when initiated by a No. 6 mercury fulminate-potassiumchlorate detonator, the freshly made explosive detonates with a velocityof about 3,400 metres per second. This explosive can also be initiatedby a No. 2. mercury fulminate-potassium chlorate detonator.

Example 5 A mixture of 7 parts anhydrous sodium acetate, 13 parts sodiumnitrate and 20 parts ammonium nitrate is fused together and a further39.5 parts ammonium nitrate and 0.5 part agar-agar are graduallyintroduced into the melt, which is heated on the steam bath, until nomore of the ammonium nitrate present will dissolve. 20 parts moltentrinitrotoluene are then stirred into the mixture at a temperature of atleast 95 C. until it has been emulsified. The emulsion is then pouredout and allowed to solidify in the form of a A slab, which is crushed ata temperature of 46 C. The material passing a 16 mesh B. S. S. sieve isthen packed in waxed paper containers under a pressure of 75 lbs. persquare inch. Its sensitiveness does not difier markedly from that of theexplosives described in the preceding examples.

Example 6 A mixture of 57.6 parts ammonium nitrate, 7.7 parts sodiumnitrate and 3.8 parts sodium chloride is heated until partly fused, and5.6 parts nitroguanidine, 4.8 parts guanidine nitrate and 0.5 agar-agarare then introduced and the mixture is further heated at a temperatureof C. until completely fused. 20 parts molten trinitrotoluene are thenstirred into the mixture until it has been emulsified and the fusedemulsion is then spread out into a thin layer and allowed to congeal inthat form. It is then flaked. The resulting explosive is then packed ina tin-plate contai n'er. Its sensitiveness do'es 'notdiffermarkedlyinitrate and-at least one compoundnonvolatile at the temperature of the-me1t- 'and adapted to' lower the melting point ofithe ammonium nitrate,to give a resulting emulsion which congeals'at a temperature above 46-C; and Mini-Q1118 free'f-rom uncombined water, andcongealingandgranulating' the resulting emulsion.

' 2. A process as-claimed in claim 1 wherein the emulsion is formedat atemperature DetWeen'SO" C; and 110 C.

' 3. A process as claimed in claim 1 whereinit'he;

high -explosive is trinitrotoluene.

4; A process as claimed in claim l Whereinthe non-volatile compoundadapted to lower the melting point of the ammonium nitrate comprises ananhydrous compound forming a low melting eutectic mixture with it.

' 5. A processas claimed in claim '1 whereinjt'he non-volatile compoundadapted to lower the meltingrpoint of ammonium nitrate comprises ahydrated salt.

6. A process as claimed in claim 1 whereinlthe non-Volatile. compoundcomprises a :metallic nitrate.

-7;' A' process as claimed in-claim 1 wherein the non volatile compoundis: an oxidizing salt.

1 8. A process a-s cla'imed: in claim 1 wherein the emulsi-iyingilagenti comprises-agar-agar.

9-"; A processias-clal med-in claim 1 wherein thegranulation-:-isncommenced before the emulsion has; ceoled:=sufficientlyto become substantially congealed.

= JOHN WHETSTONE.

i RE -Enemies CITED "The 'following'references are of record in the fileof this patent: V

UNITED STATES PATENTS Number Name Date- 51,242,900 ifvl'lini ng Oct. 9,1917 1;?973213 -Marin- Mar; 11,1919 1;6'Z1,'7,92 Stoops 1 'May 29, "192820; F1 ,-908';569 'stoopscnu May 9, 1933 lg9261438 --Spaeth Aug. 1,1933=1,'968,I58 I "Nadum July 31; 1-934 211635 72 "Wcbdbury 1 'Dec. 8,- 19362539;712- Cairns Sept. 20; 1938 25. 2,199,218 GU01; "Apr.'30, 1940 253535147 Y Cook 1 July -11, "19% 2309 2919 'vlhetstone .1 Oct. 22, 1946Number country I Date "384,966 Great-Britain i "Dec. 15, 1933 53E579,GreatnBritain June 27, 1941 #552,645 Great-Britain Apr.:19', 1943

